1. Field of the Invention
The invention relates to an arrangement for the temperature-compensated multi-dimensional micropositioning of mutually position-defined optical components, comprising a guide unit for housing the optical components as well as several piezo actors.
2. Discussion of the Background
With Fabry Perot interferometers it is known to utilise multiple reflections in a gaseous medium with a constant refractive index, with the gaseous medium being enclosed by two permeable plates which are metal-coated on one side and aligned parallel to each other. It is between the two mirror plates, where the mentioned evaluable multiple reflections occur. Depending on the mirror distance, a constructive interference and transmission takes place for one wavelength only. In this manner it is possible to investigate a wavelength range of a few nanometers, the so-called free spectral range, with a very small motion of the mirror plates towards each other, and thus determine even the most minute displacements or increases of individual spectral lines. The mirror plate distance can be adjusted in a more or less controlled manner by means of piezo elements.
From Optical Engineering Vol. 37, No. 4, Apr. 7, 1998, pages 1229 to 1234, various piezoelectric actors for optical applications are known. For example, a so-called piezo actor of the stack type is presented therein, which consists of a stack arrangement of individual elements connected in series. It is possible with such stack-type actors to realize relatively large adjustment travels. For a two-dimensional adjustment cylindrical actors or actors arranged in parallelogram shape are of the related art, while for the detection of the current position the integration of preferably optical sensors is also known, in order to enable a controlled piezo motion, in particular with optical systems.
It was found, however, that the previously introduced length-variable actors consisting of guide unit and piezo drive do not adequately meet the special requirements, in particular with respect to the necessary temperature stability and temperature independence. An improvement of the tilt, wear, and clearance-free motion of optical components relative to one another is generally achieved only with a prohibitive cost increase which leads to considerably higher costs of measuring and test equipment to be manufactured.
Based on the above, it is therefore the object of the invention to specify an advanced arrangement for the temperature-compensated multi-dimensional micropositioning of mutually position-defined optical components, by means of which a particulary economic mechanical guide system can be presented which is of a simple construction and thus technologically feasible in an easy manner.
Accordingly, the basic idea of the invention is to realise the guide unit of the arrangement for the temperature-compensated multi-dimensional micropositioning of optical components, from two spaced plates or rings, with several spaced solid joints being arranged between the rings or plates. The solid joints can be integrated in bolt-type connection means of the guide unit or comprise same. The guide unit with plates, bolts and/or solid joints can be formed both by joining together several individual components and in a monolithic manner, i.e. integrally.
Piezo actors are secured in a neighbouring relationship with the solid joints or bolts, respectively, in such a manner that actuation or positioning forces, respectively, can be made to act on the rings or plates.
At least the surfaces of the rings or plates accommodating the optical components, i.e. the outer end faces, are coated with a material corresponding to that of the optical components, with the coating being able to be machined in a suitable manner prior to snapping-on the optical components for a definite positional definition. According to the invention, the guide unit and the optical components are made from materials with essentially the same temperature coefficients. The material if the guide unit is preferably Invar, and the material of the optical components is quartz or quartz glass, respectively. The coating is also realised from quartz, e.g. by sputtering or vapour deposition or similar coating methods. The coating layer may be machined in a suitable manner, e.g. polished, for maintaining the desired mutual positions of the optical components.
The inner surfaces of the plates or rings comprise several distributed conductive areas each of which forming capacitive sensors for the detection of location and/or positional variations of the plates or the optical components, respectively, attached thereon.
In an embodiment of the invention, the plates or rings each have an essentially central opening or through-hole, with the respective rear side or an integral extension of the optical component covering or passing the opening. At the rear side or the face of the extension, several distributed conductive areas are arranged which, together with the opposite areas form capacitive range sensors each, so that a control loop for controlling the piezo actors can be realised in a simple manner.
The circumference of the guide unit preferably comprises three equally spaced solid joints or bolts comprising such joints, with one piezo actor each being arranged between two solid joints or bolts, respectively.
As already mentioned, control signals for the operation of the piezo actors can be derived from the location and positional variation values of the capacitive sensors, so that the desired actuation position can be maintained or a new position can be adjusted upon feedback.
The solid joints and piezo actors are preferably arranged or secured in an alternating manner spaced by 120xc2x0 between the plates or rings. The capacitive sensors or sensor areas, resspectively, are also designed to be spaced by essentially 120xc2x0 each, with associated areas representing a measuring capacitor being arranged opposite to one another.
As the piezo actors, piezo stack arrangements can be used wich are individually controllable.
All materials employed are adapted to one another in such a manner that upon temperature influences on the actor unit no changes in distance of the optical components from each other occur. The connection between the guide unit and the optical parts or components can be realised for example by a sputtered layer, with this layer consisting of the material of the optical components themselves. The applied connecting layers can be high-precision ground parallel to one another prior to the final securing of the optical components so that a defined initial position of the optical components is given after their attachment to the arrangement, e.g. by snapping-on. The capacitive sensors fields or sensor areas at the inner faces of the optical components or the extension, respectively, but also of the rings or plates can be generated by sputtering, vapour deposition, or cluster deposition.
With the introduced arrangement, the invention unites optimum sensorics which is inherent with the system and does not require any additional installation space or detrimentally influences the desired properties of the optical components with a straight-forward temperature-compensated design. Specifically and with respect to the latter aspect, previously required multi-layer intermediate coatings have been omitted, which are disadvantageous not only because of temperature stability considerations but, in addition, involve higher technological expenditures.